Man, I feel for you. I had a mated pair of Osc clowns and a mated pair of Clarkiis in two separate tanks. I lost my female Osc and male Clarkii in the same week, not sure what killed the Osc but the Clarkii jumped. Both pair had been laying eggs regularly. I wanted to get rid of the Clarkii's, so I haven't tried to pair my female back up.
My osc, however, I immediately got a similar sized osc. Big mistake. My male decided he wanted to be dominant (female) and beat the holy crap out of the new one, nearly killing it. After about two weeks the dominance seemed settled and the newcomer healed up nicely. Now my former male is the female, the new one is male, and they're hosting in my bta. No sign of eggs yet but they're definitely paired.
So, that said, my advice is not to worry about timing for getting a new mate, but worry more about size. Since you lost a male, make sure that your replacement comes from a tank with many clowns in it and that your candidate is one of the smaller ones, which should insure it's male. Get him home quick and introduce them. Make sure there are tons of hiding places in the tank, don't freak out if there seems to be a bit of violence, and everything should work itself out. Keep in mind that any clown left alone will assume dominance and become female, so any clown you add after should be smaller. When they're similar size they fight it out, when one is significantly larger than the other it's usually less of a contest.
Make sure to do the changes you discussed to prevent it happening again, and good luck!